Synthetic resin multicellular product whose main component is acrylonitrile and process for preparation thereof

ABSTRACT

Process for preparing multicellular products which comprises mixing urea and/or a urea derivative, and an acid with a monomeric mixture comprising 60-95 percent by weight of acrylonitrile and 40-5 percent by weight of a vinyl monomer copolymerizable with acrylonitrile, polymerizing the mixture with the use of catalyst and/or by irradiation, and thereafter heating the resulting polymer at 100*-250* C.; and multicellular products produced by the above process, in which fine cells having an average diameter of less than 1.0 mm are substantially uniformly dispersed in the polymer and which product has a specific gravity of less than 0.3 g/cm3.

Sagane et al.

[ June 27, 1972 SYNTHETIC RESIN MULTICELLULAR PRODUCT WHOSE MAINCOMPONENT IS ACRYLONITRILE AND PROCESS FOR PREPARATION THEREOFInventors: Norio Sagane, Kyoto; Issei Kuwazuru; Isao Kaetsu, both ofOsaka-fu, all of Japan Assignee: Sekisui Kagaku Kogyo Kabushiki KaishaFiled:- Dec. 19, 1969 Appl. No.: 882,783

Related U.S. Application Data Continuation of Ser. No. 603,777, Dec. 22,1966, abandoned.

Foreign Application Priority Data References Cited 1 UNITED STATESPATENTS 4/1953 Glenn ..260/2.5 11/1966 Ingram et al. 3,304,274 2/1967Eng 3,513,112 5/1970 Kanai et al ..260/2.5

FOREIGN PATENTS OR APPLICATIONS 1,368,383 6/1964 France ..260/2.5 N

Primary Examiner-Murray Tillman Assistant Examiner-Morton FoelakAnorneywenderoth, Lind & Ponack [57] ABSTRACT Process for preparingmulticellular products which comprises mixing urea and/or a ureaderivative, and an acid with a monomeric mixture comprising 60-95percent by weight of acrylonitrile and 40-5 percent by weight of a vinylmonomer copolymerizable with acrylonitrile, polymerizing the mixturewith the use of catalyst and/or by irradiation, and thereafter heatingthe resulting polymer at 100-250 C.; and multicellular products producedby the above process, in which fine cells having an average diameter ofless than 1.0 mm are substantially uniformly dispersed in the polymerand which product has a specific gravity of less than 0.3 g/cm.

8 Claims, No Drawings SYNTHETIC RESIN MUL'I'ICELLULAR PRODUCT WHOSE MAINCOMPONENT IS ACRYLONITRILE AND PROCESS FOR PREPARATION THEREOF Thisapplication is a continuation of Ser. No. 603,777, filed Dec. 22, 1966,now abandoned.

This invention relates to a synthetic resin multicellular product whosemain component is acrylonitrile and a process for the preparationthereof.

By the conventional processes for the preparation of multicellularproducts, various synthetic resin multicellular products such as phenolresin, urea resin, polyurethane resin, epoxy resin, silicone resin,natural rubber, cellulose acetate, polyethylene and vinyl resins such aspolystyrene, polyvinyl chloride and polyvinyl formal have been prepared.

And these synthetic resin multicellular products have been put on themarket in soft, semihard and hard forms having continuous foam anddiscontinuous foam and broadly used in the fields of building materialand packing material.

As processes for the preparation of such" synthetic resin multicellularproducts, the following processes are well known.

1. A process of foaming a molten'resin or a suspension or solution of aresin or introducing a gas with mechanical stirring and fixing bubblesby the action of heat or a catalyst.

2.- A process of dissolving a proper volatile substance in a resincomposition, thereafter raising the temperature or raising thetemperature and reducing the pressure thereby gasifying the volatilesubstance into a gaseous or vapor state and changing the resincomposition into a foaming structure, thereafter fixing bubbles bycooling or chemical action.

3. A process of retaining a discharged gas inside a resin composition bychemical reaction between or among the components of a resin-formingcomposition or heat decomposition of a decomposition-type blowing agentaccompanied by generation of gas.

In spite of the fact that various synthetic resin multicellular productsand processes for the preparation thereof are known as such, it isworthy of attention that a synthetic resin multicellular product whosemain component is acrylonitrile has not been known.

Polyacrylonitrile is almost insoluble in an ordinary organic solvent,and when heated it is not melted and softened, but discolored anddecomposed and cannot be made a softened state suitable for shaping andprocessing ordinary thermoplastic resins, there being no proper foamingprocess, because of that despite its various characteristics such asexcellent chemical resistance, water resistance, heat resistance andmechanical strength concurrently and inherently possessed bypolyacrylonitrile, it has not been utilized in the preparation of amulticellular product.

With a view to solving these difficulties in shaping and processingpolyacrylonitrile thereby obtaining a synthetic resin maintainingexcellent chemical resistance, heat resistance and mechanical strength,attempts have been made to obtain synthetic resins by copolymerizingacrylonitrile with various other vinyl monomers, however, a copolymerwhose main component is acrylonitrile is, similar to polyacrylonitrile,discolored and decomposed when heated and it is difficult to make thecopolymer into a softened state suitable for shaping and processing.This inclination increases as the content of acrylonitrile in thecopolymer components increases. In fact,

when the content of acrylonitrile became more than 60 percent by weight,it has been almost impossible to make the polymer into a softened statesuitable for shaping and processing.

Due to such difficulties, it was not possible to uniformly mix a blowingagent in the resin or foam the resin by heating, and as a multicellularproduct having acrylonitrile as a component, anacrylonitrile-styrene-butadiene copolymer and acrylonitrile-styrenecopolymer whose acrylonitrile component are little, are known.

An object of this invention is to provide a novel synthetic resinmulticellular product whose main component is acrylonitrile.

thermoplastic resin multicellular product and having an excel-' lentmechanical strength not obtained by the conventional thermo-settingresin multicellular product.

A further object of this invention is to provide a multicellular producthaving fine cells and a good water resistance.

A still further object of this invention is to provide a multicellularproduct whose cutting processability has been improved.

One of other objects of this invention is to provide a multicellularproduct having little discoloring and a large foaming magnification.

Another of other objects of this invention is to provide a process forthe preparation of the aforementioned multicellular product.

Other objects and advantages of this invention will become" vinylmonomer copolymerizable with acrylonitrile, especially such vinylmonomer as methyl methacrylate, methyl acrylate,

styrene, vinyl acetate, methacrylarnide and acrylamide, in saidcopolymer fine cells whose average diameter is below 1.0 mm aresubstantially uniformly dispersed, said multicellular product has aspecific gravity of below 0.3.

Such multicellular product is obtained by a process which comprisesadding urea or a urea derivativesand an acid, preferably water also to amixture of 60-95 percent by weight of acrylonitrile and 40-5 percent byweight of a vinyl monomer copolymer copolymerizable with acrylonitrileunifonnly to mix the all, followed by polymerization by a catalyst or anionizing radiation to prepare a foamable polymer, thereafter heating thepolymer to l0O-250 CL, preferably l50-200 C.

A vinyl monomer copolymerizable with acrylonitrile as referred to inthis invention points toat least one-monomer selected fromthe class ofvinyl monomers each having one vinyl group. And as such monomer, theremay be cited, for instance, methacrylic acid ester, acrylic acid ester,methacrylic acid, acrylic acid, acrylamide, methacrylamide,methacrylonitrile, crotonitrile, styrene, styrene derivative, vinylacetate and aryl ester.

The properties of a multicellular product obtained by the process ofthis application vary depending upon the kind of such vinyl monomer, anda vinyl monomer such as methacrylic acid ester, acrylic. acid ester andvinyl acetate will give a finely foamed multicellular product withlittle discoloring having a good water resistance.

A vinyl monomer such as styrene and vinyl toluene will give amulticellular product of somewhat large cells having excellent cuttingprocessability by machines. And when acrylarnide or methacrylarnide isused, it will remarkably prevent discoloring of a multicellular productand a multicellular product having a large foaming magnification andexcellent heat resistance and mechanical strength is obtained.

Acrylic acid and methacrylic acid will give a multicellular producthaving a large foaming magnification similar to acrylarnide andmethacrylamide, however, the multicellular product becomes inferior inwater resistance. Generally, a hydrophilic vinyl compound such asacrylic acid and methacrylic acid having such property as mentionedabove, in order to prepare a multicellular product required to be waterresistant, hydrophilic vinyl monomers are undesirable except acrylarnideand methacrylarnide and it is better to use hydrophobic vinyl monomers.

In order to obtain a multicellular product having a large foamingmagnification as well as excellent heat resistance and water resistance,combination of methyl methacrylate and small amount of acrylamide willgive a good result.

In this invention, a vinyl monomer copolymerizes with acrylonitrile toform a copolymer containing therein urea or a urea derivative, an acidand water. When this copolymer is foamed by heating to prepare amulticellular product, the vinyl monomer plays a useful role of makingthe copolymer into such a softened state as is capable of expendingwithout substantially decomposing the copolymer. When the amount of avinyl monomer is made below percent by weight, at the time of heatingand foaming, the copolymer is remarkably discolored and decomposed and amulticellular product having a large foaming magnification is notobtained. On the other hand, when the amount of a vinyl monomer is madeabove 40 percent by weight, a multicellular product will be inferior inheat resistance and chemical resistance and not greatly different fromthe conventional thermoplastic resin multicellular product. Therefore,both of the two instances will not enable one to achieve the object ofthis application.

I .From the foregoing reasons, in this invention when the content ofacrylonitrile is made 60-95 percent by weight, a goo multicellularproduct can be obtained.

In this invention, urea or urea derivatives are used as blowing agent.As urea derivatives, urea derivatives represented by the general formulaH NCONHR (wherein R stands for alkyl, cycloalkyl, acyl and phenylgroups) may be cited. As such urea derivatives, there may be cited, forinstance, a N-monoalkyl substituted product such as H NCONHC H and H N-CONHC H,, a N-monocycloalkyl substituted product CH2 such as and H NCONHHzNCHNH a. N-monoacyl subsfi tifiedproduct such as H4NC ONHC OCH3 andHQNC ONHC OCH5 and a N-monophcnyl substituted product such as H CH3 andI'IQNCONH It is also possible to use one or more substances selectedfrom thegroup consisting of urea and urea derivatives. The mixing ratioof urea or urea derivatives to the monomer mixture of the aforementionedratio is properly selected in accordance with the properties and foamingmagnification of the objective multicellular product, and notparticularly decided, however, it is preferable to make the content ofurea or urea derivatives of the entire components within the range of2-15 percent by weight.

Urea or urea derivatives or their aqueous solution cannot be dissolvedin the monomer mixture of the aforementioned ratio. When urea ispolymerized without being dissolved, but in a dispersed state, and thenmade a multicellular product, cells will become non-uniformand largewith a result that no good multicellular product is obtained. When ureaor urea derivatives are mixed with the monomer mixture of said ratiotogether with an acid, said acid will not destroy the function of theurea or urea derivatives as a blowing agent and it is possible todissolve the urea or urea derivatives with the monomer and make theentire mixture a uniform composition.

Heretofore, as decomposition-type blowing agent, ammonium carbonate,ammonium bicarbonate, sodium bicarbonate, a metal halide, a metal aziddiazoaminobenzene, PP'-oxybisbenzenesulfonyl hydrazide,NN'-dinitrosopentamethylenetetramine and azodicarbonamide have beenknown.

However, it is difficult to homogeneously dissolve these blowing agentsin acrylonitrile, and even if these blowing agents are used in theprocess for the preparation of this invention, foaming will becomenomuniforin and they do not give a good multicellular product. And as inthis invention, when an acid is added each of these blowing agents willbe decomposed immediately and the role as a blowing agent will not beplayed after the polymerization.

As an acid used in this invention, inorganic acid and organic acidordinarily used are usable, however, preferably an acid beingnon-volatile at room temperature under atmospheric pressure having adissociation constant of above is usable. As such preferable acid, theremay be cited such inorganic IIzNC ONI-I acid as sulfuric acid, nitricacid, phosphoric acid and pyrophosphoric acid and such organic acid asformic acid, acetic acid, propionic acid, n-butyric acid, iso-butyricacid, caproic acid, glycolic acid, chloropropionic acid,monochloroacetic acid, trichloroacetic acid, lactic acid,trichlorolactic acid, benzoic acid, salicylic acid, dioxybenzoic acid,cyclohexyl carboxylic acid, toluic acid, benzenesulfonic acid,phenolsulfonic acid and toluene-sulfonic acid may be cited. Especially,sulfuric acid, phosphoric acid, pyrophosphoric acid, formic acid, aceticacid, propionic acid and benzoic acid are preferable.

When sulfuric acid'and formic acid are used, foaming magnification of amulticellular product is increased and it is possible to make amulticellular product having fine foams. The use of phosphoric acid isefi'ective to make a multicellular product non-inflamable.

Inthis invention, an acid works efiectively for uniformly andhomogeneously dissolve urea and urea derivatives in the monomer mixtureof said ratio without damaging properties of the urea of ureaderivatives as blowing agent, and the mixing amount of the acid isdecided depending upon the mixing amount of the urea or ureaderivatives. The acid is added in an amount necessary for dissolvingurea or urea derivatives in the monomer or an amount exceeding saidamount. However, when the amount of the acid becomes too large, it isundesira-.

ble because the obtained multicellular product becomes brittle as aresult. Preferably, the amount of the acid is within the range of 10-45percent by weight based on the entire components.

In this invention, a mixed composition of acrylonitrile, a vinyl monomercopolymerizable with acrylonitrile, urea or urea derivatives and an acidmay be copolymerized, however, water may be further added. When water isadded, it is possible to increase the foaming magnification of theobtained multicellular product and lessen discoloring ofthe-multicellular product due to heat decomposition.

The reasonwhy foaming magnification is increased and discoloring can beprevented when water is added, is not clear, however, it is consideredthat water assists decomposition of urea or urea derivatives at afoaming temperature and a part of nitrile group (-CN) in the copolymeris convertedto amide group (-CONH,) due to coexistence with waterthereby discoloring of the multicellular product is prevented.

The adding amount of water is properly selected in accordance with theproperties of the desired multicellular product. However, when theadding amount of water becomes excess, water is not homogeneouslydissolved in said mixed composition, therefore, it is necessary to add awater in an amount in such range within which water is homogeneouslydissolved in said mixed composition. Even when a large amount of wateris added, an acid being further added, it is possible to homogeneouslydissolve them in said mixture, however, in that case, foams, of theobtained multicellular product becomes rough, the multicellular productbecoming brittle and weak in water resistance, therefore, it is notdesirable.

Therefore, it is preferable to make the adding amount of water below 10percent by weight based on the entire components.

Also in the composition, filler, dyestuff, pigment and discoloringprevention agent may be properly mixed.

In the process of this invention, a mixed composition, as mentionedabove, of acrylonitrile, vinyl monomer copolymerizable withacrylonitrile, urea or urea derivatives,

an acid and water if necessarily is polymerized and made a foamablepolymer.

As a process for the polymerization, a process generally used forpolymerization of a monomer may be properly adopted and a process forthe catalytic polymerization, a process for the radiation polymerizationand conjoint use of a process for the catalytic polymerization and aprocess for the radiation polymerization are preferably usable. I

Upon carrying out catalytic polymerization, an ordinarily usedpolymerization initiator is usable, and a catalyst such asazobisisobutylonitrile and benzoyl peroxide and a polymerizationinitiator of the redox system are preferable.

As such polymerization initiator of the redox system, a polymerizationinitiator consisting of combination of benzoyl peroxide,t-butylhydroperoxide and decumyl peroxide with N,N'-dimethylaniline,nitrotryspropionamide, dimethylaminopropionitrile, sodium ascorbatetriethylarnine and triethanolamine are preferably usable.

Also upon carrying out catalytic polymerization; a process wherein atfirst polymerization is carried out at a temperature below 40 C. untilthe composition becomes solid state, thereafter the temperature israised to above 40 C. thereby completing the polymerization ispreferable.

In case the volume of a polymer is large, when a polymerization processof the radiation polymerization or conjoint use of catalyticpolymerization and radiation polymerization is used, control ofpolymerization heat becomes easy and it is possible to carry out apolymerization at a low temperature.

A polymer obtained by such polymerization process contains therein ureaor urea derivatives, an acid and water uniformly and integrally, beingpreferable to make a multicellular product by heating per se to foam.

However, in the case of improper mixing ratio of urea or ureaderivatives with an acid or unsuitable polymerization conditions,sometime bubbles are brought about in the polymer. The bubbles make amulticellular product nonuniform and its decreases a good property of amulticellular product when the polymer is heated to prepare amulticellular product later. In order to prevent such harmful bubblesfrom being brought about, it is effective to add dimethyl formamide ordimethyl sulfoxide in a small amount to the components. However, if theamount becomes excess, it will make the heat resistance of themulticellular product bad. i

In order to foam a polymer obtained by said polymerization process andmake a multicellular product, the polymer is heated to such atemperatureat which the polymer expands by a generated gas withoutsubstantially decomposing. It is preferable to make the heatingtemperature l00250 C., preferably l50-200 C.

By heating the urea or urea derivatives in said polymer decomposes,generating gas. The polymer reaches a softened state where it expands bya generated gas and comes to form a multicellular product. The acid andwater in said polymer help decomposing urea or urea derivatives andprevent the polymer from discoloring by decomposition, making itpossible to prepare a multicellular product whose main component isacrylonitrile.

in the process of this invention by using an acid together with blowingagent it is possible to uniformly and homogeneously dissolve a blowingagent in a mixture of acrylonitrile and a vinyl monomer copolymerizablewith acrylonitrile without destroying the function as a blowing agent.Because polymerization is carried out after uniformly dissolving ablowing 'agent in a monomer and polymers so obtained include finelydispersed blowing agent, it is possible to make a multicellular producthaving a homogeneous fine cell whose diameters are below 0.001 mm.

In accordance with the process for the preparation of this invention,foaming is effected by heating the polymer to a temperature suitable forfoaming in the presence of an acid and water, therefore, decompositiondiscoloring of acrylonitrile can be prevented and it is possible to makea multicellular product have a good appearance.

Also because the multicellular product of this invention consists ofacrylonitrile as its main component, it is excellent in heat resistanceenduring the constant temperature of 160-180 C., also excellent in waterresistance, chemical resistance and mechanical strength. 7

Next, Examples of this invention will be shown. Parts in Examples meanparts by weight.

EXAMPLE 1 One hundred parts of acrylonitrile, 50 parts of methylmethacrylate, 15 parts of urea, 31 parts of benzoic acid and 24 parts ofmonochloroacetic acid were mixed and stirred to obtain a uniformtransparent solution.

After polymerizing this solution by radiating 5.9 X 10 roentgens of agamma ray (cobalt 60) having a strength of 4.7 X 10 reontgens/hour, theso obtained polymer was heated at 180 C. for 15 minutes, as a result20-time expanded yellow colored multicellular product was obtained.

This multicellular product had an average cell diameter of 0.89 mm and aspecific gravity of 0.06.

When this multicellular product was used for a long period of time at160 C., it did not shrink, being excellent in heat resistance.

EXAMPLE 2 One hundred parts of acrylonitrile, 50 parts of methylmethacrylate, 15 parts of urea and 33 parts of glacial acetic acid weremixed to obtain a uniform transpa'rentsolution.

After polymerizing this solution by irradiation a dose of 5.9

X 10 roentgens of a gamma ray having a dose rate of 4.7 X 10roentgens/hour, and heating the so obtained polymer lump in a constanttemperature over at l C. for 15 minutes, a 25- time expanded lightyellow multicellular product was obtained. I

This multicellular product had an average cell diameter of 1.0 mm and aspecific gravity of 0.048.

EXAMPLE 3 One hundred parts of acrylonitrile, 40 parts of methylmethacrylate, 5 parts of urea, 17.2 parts of a percent sulfuric acidwere mixedto obtain a transparent solution.

To this solution, 0.5 percent by weight based on this solution each ofbenzoyl peroxide and N,N-dimethylaniline was added and polymerizationwas carried out at 35 C. for 12 hours in a polymerization vessel havingan internal capacity of 20 mm X 240 mm X 300 mm to obtain a polymer of asize of l5mmX240 mm 300mm. I

Thereafter, when this copolymer was heated in a constant temperatureoven at 190 C. for 15 minutes, a light yellow fine foamed multicellularproduct having a specific gravity of 0.037, a foaming magnification of32 times, and an average cell diameter of 0.01 mm was obtained.

This multicellular product had. excellent mechanical strengths of abending strength of 10 kg/cm a tensile strength of 13 kg/cm and a 50percent compressed strength of 8 kglcm at the same time, exhibiting ahigh heat resistance of enduring a long use at C.

EXAMPLE 4 One hundred parts of acrylonitrile, 40 parts of methylmethacrylate, 5 parts of urea, 27 parts of trichloroacetic acid, 5 partsof a 85 percent phosphoric acid and 4 parts of water were mixed toobtain a transparent solution.

To this solution, 1 percent by weight based on this solution each oftertiary butylhydroperoxide and N,N'-dimethylaniline was added,polymerization was carried out at 40 C. for 16 hours and at 50 C. for 10hours, and the obtained polymer was foamed by heating at C. to obtain a35-time expanded light yellow multicellular product having a fine cellstructure.

This multicellular product had an average cell diameter of 1 mm and aspecific gravity of 0.034.

EXAMPLE 5 One hundred parts of acrylonitrile, 40 parts of methylmethacrylate, 5 parts of urea, 20 parts of benzoic acid and 10 parts ofa 70 percent n-lactic acid aqueous solution were mixed to obtain atransparent solution.

To this solution a dose of 2 X 10 roentgens of a gamma ray having a doserate of l X 10 roentgens/hour was irradiated, and the obtained polymerlump was heated to 200 C. to foam and alight yellow multicellularproduct having fine cells were obtained.

The properties of this multicellular product were almost same as thoseof what was obtained in Example 3.

EXAMPLE 6 One hundred parts of acrylonitrile, 40 parts of methylmethacrylate, parts of phenylurea, 7.5 parts of a 95 percent sulfuricacid and 10 parts of a 50 percent benzenesulfonic acid aqueous solutionwere mixed to obtain a transparent solution.

Polymerization was carried out by irradiating a dose of 3.5 X 10roentgens of a gamma ray having a dose rate of l X 1 roentgens/hour, theobtained polymer was heated to 200 C. and a light yellow multicellularproduct having a fine cell structure, a specific gravity of 0.04, afoaming magnification of 30 times and an average cell diameter of 0.01mm. was obtained.

EXAMPLE 7 One hundred parts of acrylonitrile, 25 parts of methylmethacrylate, parts of styrene, 10 parts of urea, 34 parts of a 95percent sulfuric acid, 3 parts of water and parts of a 85 percentphosphoric acid were mixed, to obtain a transparent solution, 1 percentof benzoyl peroxide and 1 percent of N,N'- dimethylaniline by weightbased on said solution were added to the obtained transparent polymer.Polymerization was carried out at 40 C., thereafter the obtained polymerwas heated to 180 C. to foam, and a multicellular product having afoaming magnification of 42 times was obtained.

This multicellular product had a specific gravity of 0.02 and an averagecell diameter of 0.028 mm.

This multicellular product had a very excellent cutting processabilitysimilar to that of ordinary lumber, ordinary wood-working machines.

EXAMPLE 8 One hundred parts of acrylonitrile, 30 parts of methylacrylate, 20 parts of vinyl toluene, 35 parts of a 95 percent sulfuricacid, 5 parts of urea and 5 parts of cresol were mixed, to the obtainedtransparent solution a dose of 2.5 X 10 roentgens of a gamma ray havinga dose rate of 1 X 10 roentgens/hour were irradiated to carry outpolymerization. When the obtained polymer was heated at 180 C. for 30minutes, an about 23-time expanded light yellow multicellular productwas obtained. This multicellular product had cell diameters of 0.05-0.1mm and a specific gravity of 0.052.

EXAMPLE 10 One hundred parts of acrylonitrile, 20 parts of butylacrylate, 20 parts of vinyl acetate, 35 parts of a 95 percent sulfuricacid, 5 parts of urea and 5 parts of cresol were mixed and homogeneouslydissolved. Thereafter, to this mixed solution a dose of 3.0 X 10roentgens of a gamma ray having a strength of 1.0 X 10 roentgens/houremitted from cobalt 60 source were irradiated to carry outpolymerization, thereafter, when the obtained polymer was heated at 170C. for 20 minutes, a light yellow multicellular product expanded about17 times having a specific gravity of 0.08 and cell diameters of 0.1-0.3mm was obtained.

EXAMPLE 1 1 One hundred parts of acrylonitrile, 15 parts of methylmethacrylate, 50 parts of a 95 percent sulfuric acid and 5 parts of ureawere mixed and homogeneously dissolved, thereafter the mixed solutionwas irradiated with a dose of 2.0 X 10 roentgens of a gamma ray having astrength of l X 10 roentgens/hour, whereby it was polymerized.Thereafter, when the obtained polymer was heated at 200 C. for 30minutes, a yel- EXAMPLE 12 One hundred parts of acrylonitrile, 10 partsof methyl methacrylate, 30 parts of a percent sulfuric acid, 15 parts offormic acid, 5 parts of urea and 5 parts of cresol were mixed andhomogeneously dissolved, thereafter the mixed solution was irradiatedwith a dose of 2.0 X 10 roentgens of a gamma ray having a strength of lX 10 roentgens/hour emitted from cobalt 60 source, whereby it waspolymerized. Thereafter, when the obtained polymer was maintained at atemperature of 200 C. for 30 minutes, a yellowish brown multicellularproduct expanded 4 times was obtained. This multicellular product had. aspecific gravity of 0.3 and cell diameters of below 0.05 mm.

EXAMPLE 13 One hundred parts of acrylonitrile, 40' partsof methylmethacrylate, 20 parts of acrylamide, 5 parts of maleic anhydride, 5parts of urea, 35 parts of a 95 percent sulfuric acid and 25 parts offormic acid were mixed ,and homogeneously. dissolved, thereafter themixed solution was irradiated with a dose of 2.5 X 10 roentgens of agamma ray having a strength of 0.5 10 roentgens/hour emitted from cobalt60 source, whereby it was polymerized. Thereafter, when the obtainedpolymer was heated at 180 C. for 30 minutes, a white multicellularproduct expanded about 49 times having a specific gravity of 0.02 wasobtained.

EXAMPLE 14' One hundred parts of acrylonitrile, 40 parts of methylmethacrylate, 20 parts of acrylamide, 5 parts of acrylic acid, 5 partsof urea, 40 parts of a 95 percent sulfuric acid and 10 parts of dimethylformamide were mixed and homogeneously dissolved. Thereafter, the mixedsolution was irradiated with a dose of 2.0 X 10 roentgens of a gamma rayhaving a strength of 0.5 X 10 roentgens/hour emitted from cobalt 60source, whereby it was polymerized. Thereafter, when the obtainedpolymer was heated at 180 C. for 30 minutes, a white multicellularproduct expanded about 53 times was obtained..The multicellular producthad a specific gravity of 0.022 and cell diameters of 0.240.3 mm.

In order to make clearer the effect of this invention, a case whereinthe content of acrylonitrile is more than 95 percent by :weight and acase wherein the content of acrylonitrile is less than 60 percent byweight will be shown as Controls.

CONTROL 1 One hundred parts of acrylonitrile, 5 parts of styrene, 15parts of urea and 40 parts of sulfuric acid were mixed and homogeneouslydissolved. Thereafter, the mixed solution was irradiated with a dose of2.0 X 10 roentgens of a gamma ray having a strength of 5 X 10roentgens/hour emitted from cobalt 60 source, whereby it waspolymerized'Thereafter, when the obtained polymer was heated at 180 C.for 30 minutes, discoloration was remarkable and the polymer hardlyexpanded.

CONTROL 2 Sixty parts of acrylonitrile, 90 parts of methyl methacrylate,15 parts of urea and 40 parts of sulfuric acid were mixed andhomogeneously dissolved. Thereafter, the mixed solution was irradiatedwith a dose of 2 X 10 roentgens of a gamma ray having a strength of 5 X10" roentgens/hour emitted from cobalt 60 source, whereby it waspolymerized. Thereafter, when the obtained polymer was heated at C. for15 minutes, a 20-time expanded multicellular product was obtained.

When this multicellular product was immersed in benzene, it expandedremarkably. When it was heated at 50 C. for 1 hour, it shrank to such anextent where its original shape did not remain and it was recognizedthat this multicellular product was remarkably inferior in chemicalresistance as compared with the multicellular products obtained in theExamples of this invention. The multicellular products according to thepresent invention have a wide variety of uses. Thus, inter alia, theycan be interposed between plastic plates of ships or rolling stock orreservoir tanks, etc., which are made of fiber-reinforced plastics. Theyare also suitable for use as such or sandwiched in between plasticplates to form partitions for buildings and the like. They can also beused in ceiling materials and in wall materials in the same way. Otheyutilities comprise functioning as substitutes for wooden molds used incasting or vacuum shaping, for floating lids on the liquid surfaces ofoil or fuel reservoir tanks and the like; also as artificial wood formaking stage settings; etc.

what is claimed is: I

l. A process for the preparation of a multicellular product whichcomprises mixing at least one substance selected from the groupconsisting of H NCONH and H NCONHR wherein R is selected from the groupconsisting of alkyl, cycloalkyl, acyl and phenyl and at least one acidwhich is substantially nonvolatile at room temperature under atmosphericpressure and which has a disassociation constant greater than with amonomer mixture consisting essentially of 60-95 percent by weight ofacrylonitrile and 40-5 percent by weight of at least one vinyl monomerselected from the group consisting of acrylic acid ester, methacrylicacid ester, and vinyl acetate,

polymerizing the entire mixture and thereafter heating the obtainedpolymer at l00250 C to foam the polymer.

2. A process for the preparation of a multicellular product whichcomprises mixing at least one substance selected from the groupconsisting of H NCONl-l and H NCONHR wherein R is selected from thegroup consisting of alkyl, cycloalkyl, acyl and phenyl, an acid which issubstantially nonvolatile at room temperature under atmospheric pressureand which has a disassociation constant greater than 10" and water witha monomer mixture consisting essentially of 60-95 percent by weight ofacrylonitrile and 40-5 percent by weight of a vinyl monomer selectedfrom the group consisting of acrylic acid ester, methacrylic acid ester,and vinyl acetate, polymerizing the entire mixture and thereafterheating the obtained polymer at l0O-250 C to form the polymer.

3. A process according to claim 2 wherein the amount of said substanceis 2-15 percent by weight and the amount of the acid is 10-45 percent byweight based on the entire mixture before polymerization.

4. A process according to claim 2 wherein said substance is urea.

5. A process according to claim 2 wherein the polymerization is employedusing a polymerization catalyst.

6. A process according to claim 2 wherein the polymerization is carriedout by irradiating said mixture.

7. A process according to claim 2 wherein the polymerization is carriedout using a polymerization catalyst and irradiating the mixture.

8. A process according to claim 2 wherein the acid is at least onesubstance selected from the group consisting of sulfuric acid,phosphoric acid, pyrophosphoric acid, formic acid, acetic acid,propionic acid and benzoic acid.

2. A process for the preparation of a multicellular product whichcomprises mixing at least one substance selected from the groupconsisting of H2 NCONH2 and H2NCONHR wherein R is selected from thegroup consisting of alkyl, cycloalkyl, acyl and phenyl, an acid which issubstantially nonvolatile at room temperature under atmospheric pressureand which has a disassociation constant greater than 10 5 and water witha monomer mixture consisting essentially of 60-95 percent by weight ofacrylonitrile and 40-5 percent by weight of a vinyl monomer seLectedfrom the group consisting of acrylic acid ester, methacrylic acid ester,and vinyl acetate, polymerizing the entire mixture and thereafterheating the obtained polymer at 100*-250* C to form the polymer.
 3. Aprocess according to claim 2 wherein the amount of said substance is2-15 percent by weight and the amount of the acid is 10-45 percent byweight based on the entire mixture before polymerization.
 4. A processaccording to claim 2 wherein said substance is urea.
 5. A processaccording to claim 2 wherein the polymerization is employed using apolymerization catalyst.
 6. A process according to claim 2 wherein thepolymerization is carried out by irradiating said mixture.
 7. A processaccording to claim 2 wherein the polymerization is carried out using apolymerization catalyst and irradiating the mixture.
 8. A processaccording to claim 2 wherein the acid is at least one substance selectedfrom the group consisting of sulfuric acid, phosphoric acid,pyrophosphoric acid, formic acid, acetic acid, propionic acid andbenzoic acid.